The present invention generally relates to a heating and cooking apparatus, and more particularly to a heat cooking apparatus such as a grill oven range in which an electric heating means is added to a microwave oven.
A so-called grill oven range as referred to above is generally so arranged to heat an object or food article to be cooked within a heating chamber by microwave energy, and also, to form scorching or burning on the surface of the food article by heat rays of an electric heating means or electric heater.
Conventionally, for adjusting the state of scorching in the grill heating in such a grill oven range, it has been a general practice that a cook manually turns on or off the electric heater through visual examination on the surface of the food article, or sets a timer of the electric heater in addition to the heating time of the food article obtained by experience. Meanwhile, as a new practice, there has been recently proposed a method in which visible light rays from a light source are projected onto a food article being heated, and the light amount of the visible light rays reflected by the food article is detected by a photo-detector so as to judge the state of scorching based on the variation with time of the detection signal, whereby heating by the electric heater is suspended upon arrival at a predetermined state of scorching, as disclosed, for example, in Japanese Patent Laid-Open Publication Tokkaisho No. 58-140524 or Tokkaisho No. 57-150731.
Although the above new practice is an epoch-making process in that the reduction of light amount of the reflected visible light rays favorably corresponds to the progress of scorching, there is such a disadvantage that, in spite of the fact that shapes of food articles to be subjected to the grill heating differ and there is a large difference in the food article color before and after the heating as in meat and fish, etc. with consequent variations in the reflected light amount, no particular countermeasures are taken therefor, and only the reflected light amount is regarded as a judging standard of the state for scorching. Accordingly, it is difficult to accurately judge all the states of scorching for various food articles, thus resulting in over-scorching or insufficient scorching depending on the kinds of food articles to be dealt with.
Furthermore, in the above new practice, since a photodiode is employed as a photo-detector for detecting the reflected light amount, the detection signal tends to drift to a large extent since it is affected by high ambient temperatures in the vicinity of the heating chamber, thus requiring a cooling device or complicated temperature compensating circuit for the prevention thereof, or necessitating an amplifier due to a low level of the detection signal, with consequent complication in the construction of the apparatus and increase in cost on the whole.